1. Field of the Invention
The present invention relates to curable compositions and methods for producing tear resistant, yet soft and deformable in-the-ear products yielding the user greater comfort and durability. Additionally, the nature of the inventive soft body design provides better acoustic performance for a variety of ear canal shapes and various motion affecting the ear canal, such as head and jaw movements.
2. Brief Description of Related Technology
Hearing aids need to be durable, comfortable and reliable. Otherwise, end users may oftentimes resist their use. Durability focuses on the integrity of the material, long lasting, and integrity of the bonding of the components. Comfortability implies that the device is soft when placed in the ear canal. Reliability implies superior acoustic quality throughout the life of the device, which requires adequate sealing within the ear canal. The challenges to satisfy the comfort and reliability objectives are due to the dynamic nature of the ear canal, and the geometric alterations of the ear canal due to natural anatomical movement. The dynamic nature of the ear canal varies from person to person, and even the anatomical shape varies from ear to ear of the same person. The canal shape is geometrically altered by motion from the head and the mandible, usually causing elliptical elongation. These differences in canal shape and changes due to body movement make it difficult to achieve a comfortable and true acoustic seal.
Challenges in meeting comfort as well as durability are due to the nature of the ear canal and materials able to use. In the past, hearing aids were made from hard acrylic materials which have proven to be durable but uncomfortable. And when the device was displaced by motion, a leakage of sound pressure occurred. Attempts were made to use rubber instead of the hard acrylic materials, such as in U.S. Pat. No. 3,527,901 to Geib. Rubber is softer and more resilient than hard acrylic but it is not very comfortable and still lacks a true acoustic seal upon motion.
Attempt to use soft vinyl materials have also not been entirely successful in meeting the aforementioned characteristics. Although vinyl may be softer than rubber and offers a better acoustic seal, soft vinyl lacks durability, and in fact, after a relatively short period of time it shrinks, turns yellow and becomes hard or brittle. It is recommended in the hearing aid industry to replace vinyl components for behind-the-ear ear molds at least annually.
Silicone materials have also been used as the housing material, such as disclosed in U.S. Pat. No. 6,022,311 to Juneau et al. The '311 patent discloses a two layer silicone housing bonded with an adhesive to the plastic faceplate of the device. Although silicone has a longer wear life than vinyl materials, it lacks strong bonding properties to the plastics commonly used in hearing aid instrumentality.
Polyurethanes have in the past been used for hearing aid components. For example, U.S. Pat. No. 5,763,503 to Cowperthwaite et al. discloses a housing for an in-the-ear hearing aid made from a solid and stiff polyurethane, polyesters or polyether to support the instrumentality. The Shore D hardness is from 50 to 90. Polyurethane has been proven to provide a better acoustic seal than polyvinyl. The properties needed for the housing require a stiff, firm, harder material to support the instrumentality which conflict with the objective for softer, comfortable fit within the ear canal.
Thus, instead of focusing on the housing material, attempts have been made to supply an attachment to the housing such as a covering or sleeve. This preserves the durability of the original housing material, while adding a comfort factor. For instance, U.S. Pat. No. 4,870,688 to Voroba et al. discloses a soft, resilient covering which is affixed to the rigid bonding of the ear shell. No covering material or details on affixing the covering to the ear shell were disclosed. Another example, U.S. Pat. No. 5,002,151 to Oliveira et al., discloses a disposable sleeve made of a soft polyurethane retarded recovery foam attached to the ear piece by mating of screw threads on the sleeve and the ear piece. Unfortunately, a sleeve concept would lack durability and require continual replacement. The sleeve creates a safety concern due to the possibility of this attachment to slip off from motion in the ear canal and possibly lodging in the ear canal. The inadequacy and quality of the disposable sleeves bonded to the housing is a major concern.
Therefore, there is a need for a deformable, soft hearing aid housing, which is tear resistant, and thus, a durable, long-lasting material. It is desired that such hearing aid housing be comfortable, soft enough, and reliable to provide superior acoustics.